Wound-electrode batteries and other such laminated batteries are commonly employed in electric automobiles, hybrid cars, and other such applications where high current density and high output are sought. Progress has also been made in the development of laminated electrochemical capacitors which possess structures similar to such batteries. Laminated batteries and electrochemical capacitors include those in which sheet-like positive electrode(s), negative electrode(s), and separator(s) are layered together to form a multilayer electrode assembly; and those in which strip-like positive electrode(s), negative electrode(s), and separator(s) are laminated together in spiral fashion to form a wound electrode assembly.
Positive electrodes and negative electrodes include those comprising only metal foil (e.g., the negative electrode in a lithium battery), those in which an active material layer is formed on a current collector comprising metal foil, and those in which a current collector comprising metal foam is filled with active material. Even electrodes having active material will have a portion, usually at an edge thereof, where the metal current collector is exposed, being uncoated with active material, for connection to a current collector tab for extraction of electricity or for direct connection to a current collector terminal. In the event that this exposed metal portion forms a short circuit with the exposed metal portion of the other electrode or with the active material layer thereof, this will cause a large current to flow, and there is a possibility that the heat that is generated as a result will cause damage to the electricity-storing device. The two neighboring electrodes are arranged in opposing fashion such that the separator intervenes therebetween. However, it is possible for a short circuit to occur in such situations as when there is skewed takeup during winding or when powder that has delaminated from the electrode due to droppage or vibration during transport or use bridges the separator.
To prevent this, Patent Reference No. 1 discloses an invention in which a short circuit prevention layer is provided adjacent to the active material layer at a region uncoated with active material on the current collector foil. Furthermore, to permit lithium ions discharged from positive electrode active material to be smoothly stored within negative electrode active material during charging, nonaqueous electrolyte secondary batteries are currently designed such that the negative electrode active material layer is larger than the positive electrode active material layer and is arranged in opposing fashion with respect to the entire positive electrode active material layer. This being the case, there will necessarily be a location at which a region uncoated with active material at the positive electrode current collector foil and a region coated with active material at the negative electrode are arranged in opposing fashion such that the separator intervenes therebetween. Patent References Nos. 2 and 3 disclose inventions in which an insulating layer is formed at a portion of a region uncoated with active material at the positive electrode which is arranged in opposing fashion with respect to a region coated with active material at the negative electrode such that the separator intervenes therebetween. Furthermore, Patent Reference No. 4 discloses an invention in which a short circuit prevention layer is made noninsulating.
PATENT REFERENCE NO. 1: Japanese Patent Application Publication Kokai No. 2001-93583
PATENT REFERENCE NO. 2: Japanese Patent Application Publication Kokai No. 2004-259625
PATENT REFERENCE NO. 3: Japanese Patent Application Publication Kokai No. 2004-55537
PATENT REFERENCE NO. 4: Japanese Patent Application Publication Kokai No. 2007-95656
PATENT REFERENCE NO. 5: International Patent Application Japanese Translation Publication No. 2005-509247